feat(auth-next-client,auth-next-server): add default auth with auto-detection

Implement default authentication for auth-next-client/server packages
to provide zero-config setup for developers.

auth-next-server changes:
- Add createDefaultAuthConfig() function with optional configuration
- Auto-detect clientId based on environment (sandbox vs production)
- Auto-derive redirectUri from window.location.origin + '/callback'
- Export default client IDs and constants for consumer use
- Uses public Immutable client IDs for development convenience

auth-next-client changes:
- Update useLogin hook to accept optional config (all fields)
- Update useLogout hook to accept optional config
- Add helper functions to create complete configs with defaults
- Auto-detect clientId, redirectUri, popupRedirectUri, logoutRedirectUri
- Export default constants for direct consumer use

This enables minimal setup:
  // Server (lib/auth.ts)
  export const { handlers, auth } = NextAuth(createDefaultAuthConfig());

  // Client
  const { loginWithPopup } = useLogin();
  await loginWithPopup(); // No config needed!

  const { logout } = useLogout();
  await logout(); // No config needed!

Consumers can still override any field as needed for production use.

Related to wallet package default auth implementation (PR #2768).

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: rodrigo-fournier-immutable

packages/auth-next-client/src/constants.ts

@@ -43,3 +43,17 @@ export const DEFAULT_TOKEN_EXPIRY_MS = DEFAULT_TOKEN_EXPIRY_SECONDS * 1000;
  * Matches TOKEN_EXPIRY_BUFFER_SECONDS (60s) in @imtbl/auth-next-server.
  */
 export const TOKEN_EXPIRY_BUFFER_MS = 60 * 1000;
+
+/**
+ * Default Client IDs for auto-detection
+ * These are public client IDs for Immutable's default applications
+ */
+export const DEFAULT_PRODUCTION_CLIENT_ID = 'PtQRK4iRJ8GkXjiz6xfImMAYhPhW0cYk';
+export const DEFAULT_SANDBOX_CLIENT_ID = 'mjtCL8mt06BtbxSkp2vbrYStKWnXVZfo';
+
+/**
+ * Default redirect URI paths
+ */
+export const DEFAULT_REDIRECT_URI_PATH = '/callback';
+export const DEFAULT_POPUP_REDIRECT_URI_PATH = '/callback/popup';
+export const DEFAULT_LOGOUT_REDIRECT_URI_PATH = '/';